Abstract: Objective: To study the expression of 5-lipoxygenase(5-LOX) in mucoepidermoid carcinoma(MEC),and to explore its probability of acting as a referential index in the diagnosis and treatment of mucoepidermoid carcinoma.Methods: The expressions of 5-LOX in 40 cases of MEC,20 cases of normal tissue of salivary glands and 20 cases of pleomorphic adenomas were detected by EliVision^TM plus immuniohistochemical method.All the data were analyzed statistically.Results: The positive staining rate of 5-LOX in mucoepidermoid carcinoma was 67.5%,which was significantly higher than that in pleomorphic adenoma(0.0%) and normal tissue of salivary glands(5.0%) (P<0.01).The positive staining rates of 5-LOX in high-differentiated,moderate-differentiated and low-differentiated cases of MEC were 50.0%,6/9 and 100.0%,respectively.The difference was significant(P<0.05).Conclusions: 5-LOX may be used as a biology referential index in diagnosing and differentiating the degree of mucoepidermoid carcinoma.